Evaluation of Pneumococcal Load in Blood by Polymerase Chain Reaction for the Diagnosis of Pneumococcal Pneumonia in Young Children in the PERCH Study

Abstract

Background.: Detection of pneumococcus by lytA polymerase chain reaction (PCR) in blood had poor diagnostic accuracy for diagnosing pneumococcal pneumonia in children in 9 African and Asian sites. We assessed the value of blood lytA quantification in diagnosing pneumococcal pneumonia.

Methods.: The Pneumonia Etiology Research for Child Health (PERCH) case-control study tested whole blood by PCR for pneumococcus in children aged 1-59 months hospitalized with signs of pneumonia and in age-frequency matched community controls. The distribution of load among PCR-positive participants was compared between microbiologically confirmed pneumococcal pneumonia (MCPP) cases, cases confirmed for nonpneumococcal pathogens, nonconfirmed cases, and controls. Receiver operating characteristic analyses determined the "optimal threshold" that distinguished MCPP cases from controls.

Results.: Load was available for 290 of 291 cases with pneumococcal PCR detected in blood and 273 of 273 controls. Load was higher in MCPP cases than controls (median, 4.0 × 103 vs 0.19 × 103 copies/mL), but overlapped substantially (range, 0.16-989.9 × 103 copies/mL and 0.01-551.9 × 103 copies/mL, respectively). The proportion with high load (≥2.2 log10 copies/mL) was 62.5% among MCPP cases, 4.3% among nonconfirmed cases, 9.3% among cases confirmed for a nonpneumococcal pathogen, and 3.1% among controls. Pneumococcal load in blood was not associated with respiratory tract illness in controls (P = .32). High blood pneumococcal load was associated with alveolar consolidation on chest radiograph in nonconfirmed cases, and with high (>6.9 log10 copies/mL) nasopharyngeal/oropharyngeal load and C-reactive protein ≥40 mg/L (both P < .01) in nonconfirmed cases but not controls.

Conclusions.: Quantitative pneumococcal PCR in blood has limited diagnostic utility for identifying pneumococcal pneumonia in individual children, but may be informative in epidemiological studies.

Keywords: PCR; blood; diagnosis.; pneumococcus; pneumonia.

Figure 1.

Comparison of pneumococcal polymerase chain reaction (PCR)^a load in whole blood between microbiologically confirmed pneumococcal pneumonia (MCPP)^b cases and community controls. A, load distribution among PCR-positive children. B, Receiver operating characteristic analysis among all children, including PCR-negative children. ^aPneumococcal load (density) by PCR for the lytA gene (log₁₀ copies/mL) in whole-blood specimens. ^bMCPP defined as pneumococcus detected by culture of blood, lung aspirate, or pleural fluid, PCR of lung aspirate or pleural fluid, or BinaxNOW of pleural fluid.

Figure 2.

Percentage of children with whole-blood pneumococcal polymerase chain reaction (PCR) load >2.2 log₁₀ copies/mL by case/control group overall (A) and by site (B). Denominator numbers for (B) are provided in Supplementary Table 5. Abbreviations: BCx+, blood culture positive; Conf non-Spn, a case with any nonpneumococcal bacterial pathogen detected by blood culture, by lung aspirate culture or PCR, or by pleural fluid culture or PCR; CXR+, findings of alveolar consolidation or other infiltrates on chest radiograph; CXR-AC, findings of alveolar consolidation (with or without other infiltrates) on chest radiograph; MCPP, microbiologically confirmed pneumococcal pneumonia (defined as pneumococcus isolated from culture of blood, lung aspirate, pleural fluid, PCR of lung aspirate or pleural fluid, or detection of Streptococcus pneumoniae antigen in pleural fluid on BinaxNOW); PCR+, polymerase chain reaction positive for lytA gene; RTI, respiratory tract illness.

Figure 3.

Association between pneumococcal polymerase chain reaction (PCR) load (log₁₀ copies/mL) in nasopharyngeal/oropharyngeal (NP/OP) and whole-blood (WB) specimens among cases without evidence of prior antibiotic exposure (Abx), by microbiologically confirmed pneumococcal pneumonia (MCPP) status. PCR load (density) in NP/OP specimens >6.9 log₁₀ copies/mL (horizontal line) demarks the optimal colonization load (density) threshold for discriminating MCPP cases from all controls [13]. The shaded area to the right denotes specimens with WB pneumococcal PCR load ≥2.2 log₁₀ copies/mL. MCPP was defined as pneumococcus isolated from culture of blood, lung aspirate, pleural fluid, PCR of lung aspirate or pleural fluid, or detection of Streptococcus pneumoniae antigen in pleural fluid on BinaxNOW. Nonconfirmed cases were defined as cases without isolation of bacteria from culture of blood, lung aspirate or pleural fluid, or PCR of lung aspirate or pleural fluid. Prior antibiotic exposure was defined as serum bioassay positive, antibiotic administration at the referral facility, or antibiotic administration prior to WB specimen collection at the study facility.